Inkjet recording apparatus and inkjet recording method

ABSTRACT

When the width of a recording head is greater than the width of a recording medium having a maximum conveyable width, a recorded image corresponding to ejecting ports in the entire area of the recording head cannot be corrected. Multiple correction test patterns are recorded using ejecting ports in part of the recording head, and correction data for correcting an image corresponding to ejecting ports in the entire area of the recording head on the basis of the colorimetric result of the test patterns. In this way, image data to be recorded by the ejecting ports in the entire area of the recording head is corrected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet recording apparatus and aninkjet recording method that record an image on a recording medium byejecting ink and generating correction data on the basis of colorimetricresults of the recorded image.

2. Description of the Related Art

With an inkjet recording apparatus including recording heads having aplurality of inkjet ejecting ports (nozzles), the recorded image willhave uneven color density (nonuniform color density) due to a variationin the ejecting characteristic of the nozzles. With serial recording inwhich image recording is performed by scanning a recording head withrespect to a predetermined area on a recording medium multiple times,uneven color density can be easily prevented by multi-path recording. Onthe other hand, it is difficult to prevent unevenness in color densityby line-head single path recording in which an image is recorded in onescanning operation using a wide line head having a nozzle arraycorresponding to the width of a sheet.

To improve the quality of an image recorded with a line head, it isimportant to correctly measure and analyze the color density evennessand perform correction (output correction) during recording on the basisof the measurement and analysis results. Specifically, this is atechnique that provides a high quality image by recording test patternsusing the nozzles, measuring the color density through image analysis,and determining the recording color density. As such a technique,Japanese Patent Laid-Open No. 10-13674 discusses a head shadingtechnique in which information about the volume of ink ejected from eachink ejecting nozzle is acquired, and the number of recording dots ismodified in accordance with the information about ink volume.Furthermore, Japanese Patent Laid-Open No. 2000-334935 discusses atechnique in which evenness is maintained by detecting abnormal nozzlesand terminating use of such abnormal nozzles.

To correct unevenness in color density of a recorded image caused by avariation in the ejecting characteristic of nozzles, as described above,correction test patterns are recorded on the recording medium to beused, and color density data for generating correction data is acquired.At this time, there is a limit to the size of a usable recording medium.Therefore, in some cases, color density data for correcting all nozzleson a recording head may not be acquired at once. This will be describedbelow.

FIG. 1 is a schematic view of a recording head and recording media. Inthe drawing, the recording medium is conveyed in the x direction, andthe nozzle array on the recording head extends in the y direction.Details of the configuration and control of an inkjet recording head 111will be described below. The widths of recording media 112 and 113 inthe y direction depend on, for example, the product. The recording head111 is capable of recording an image on an area wider than the width ofthe recording medium. The recording head 111 has such recording as aresult of taking into consideration so-called “frameless recording” inwhich an image is record on the entire area of the recording medium, anerror in the conveying conditions of the recording medium, and themanufacturing tolerance of the width of the recording medium. Therefore,the recording head 111 is designed to have a nozzle width greater thanthe maximum width (maximum guaranteed width) of a feedable recordingmedium.

Due to the above-described reason, image data corresponding to thenozzles of the recording head 111 should be corrected, and color densitydata is acquired by recording a correction test pattern and performingcolorimetry on this. When the nozzle width of the recording head isgreater than the maximum guaranteed width, color density data for onlythe nozzles corresponding to the maximum guaranteed width can beacquired in one recording operation. When cases in which the positionsof the corrected nozzles and the recording medium are not aligned due toerror in the conveying condition of the recording medium and framelessrecording is performed are taken into consideration, there is a problemin that correcting only the nozzle corresponding to the maximumguaranteed width is insufficient.

SUMMARY OF THE INVENTION

To solve the problem described above, the present invention provides aninkjet recording apparatus configured to record an image on a recordingmedium by ejecting ink while relatively scanning a recording head withrespect to the recording medium in a direction intersecting thepredetermined direction, the recording head having a plurality ofejecting ports for ejecting ink arranged in a predetermined direction,the apparatus including a first correction-test-pattern recording unitconfigured to record a first correction test pattern using a firstejecting port group of ejecting ports continuously aligned from a firstedge of the recording head, the number of ejecting ports in the firstejecting port group being smaller than the number of the ejecting portsof the recording head; a second correction-test-pattern recording unitconfigured to record a second correction test pattern using a secondejecting port group of ejecting ports continuously aligned in thepredetermined direction, part of the ejecting ports in the secondejecting port group being selected from the ejecting ports in the firstejecting port group and from ejecting ports not included in the firstejecting port group; and a correction-data generating unit configured togenerate correction data for correcting the image data corresponding toejecting ports included in the first ejecting port group and the secondejecting port group on the basis of a colorimetric result of the firstcorrection test pattern and a colorimetric result of the secondcorrection test pattern.

According to the present invention, the correction test pattern isrecorded multiple times at positions where the recording head and therecording medium are at different relative positions. In this way, datafor correcting nozzles of a recording head having a width greater thanthe width of a feedable recording medium.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the relationship between an inkjet printer and arecording medium.

FIG. 2 illustrates an inkjet printer forming a color image.

FIG. 3 is a schematic view of the internal configuration of a printer.

FIG. 4 illustrates the operation of simplex printing.

FIG. 5 illustrates the operation of duplex printing.

FIG. 6 illustrates an example system configuration.

FIG. 7 illustrates the flow of a process.

FIG. 8 is a block diagram illustrating an example configuration of animage processing unit.

FIG. 9 illustrates a flow.

FIGS. 10A and 10B illustrate a test pattern and a pattern required forposition detection.

FIGS. 11A and 11B illustrate recording of a test chart at multiple headpositions.

FIGS. 12A and 12B illustrate scanning color density of a test chartprint chart.

FIGS. 13A and 13B illustrate the color density characteristic of thetest chart print chart.

FIG. 14 illustrates processing carried out on an overlapping area.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detail belowwith reference to the drawings. First, analysis of the color density ofa printed image and output value correction by an inkjet recordingapparatus will be described.

Basic Configuration of Inkjet Recording Apparatus

FIG. 1 illustrates a relationship between an inkjet recording apparatusand recording media. A recording head 111 can move in the direction(y-direction) indicated by arrow 115. Recording media 112 and 113 havedifferent widths in the y direction. Hereinafter, the recording mediaare referred to as “recording paper.” However, the recording media arenot limited to paper. In this embodiment, the recording paper 112 is arecording medium having the maximum size conveyable by the inkjetrecording apparatus and having a width of 12 inches. The recording head111 has a 12.9 inch nozzle width to allow errors due to paper cutting,change by extension and contraction of the recording paper due totemperature and/or humidity, and conveying errors. If the conditions arethe same, a scanner 317, which is a reading device, may have a widththat is the same as that of the recording head 111.

FIG. 2 illustrates an inkjet recording apparatus that can record colorimages. An inkjet recording apparatus main body (printer) 100 isillustrated in the drawing. Recording heads 101 to 104 of the recordinghead 111 and respectively eject black (K), cyan (C), magenta (M), andyellow (Y) ink to record an image on recording paper 106. A line-feedmotor 105 conveys the recording paper 106 in the x direction, which isthe direction indicated by the arrow and orthogonal to the y direction.In this embodiment, the recording heads 101 to 104, respectively forKCMY ink, each have a plurality of ejecting ports (nozzles), which iseach a minimum unit for ink ejecting and arranged along the y direction(or a predetermined direction). The recording heads 101 to 104 are eachcapable of recording an image on an area corresponding to the lateralwidth (y direction width) of the recording paper 106. Hereinafter, arecording head having such a configuration is referred to as “longhead.” By performing one ink ejecting operation with each of the CMYKrecording heads 101 to 104, one raster of the output image is formed. Byrepeating the ink ejecting operation in synchronization with theconveying of the recording paper 106 by the line-feed motor 105, animage is formed on an entire page.

FIG. 3 is a schematic sectional view of the inner configuration of theinkjet recording apparatus. The inkjet recording apparatus according tothis embodiment is a high-speed line printer capable of simplex andduplex printing and uses a continuous sheet wound into a roll as arecording medium. The main components disposed inside the printer are asheet feeding unit 1, a decurling unit 2, a skew correction unit 3, aprinting unit 4, an inspecting unit 5, a cutter unit 6, an informationrecording unit 7, a drying unit 8, a sheet winding unit 9, an ejectionconveyance unit 10, a sorter unit 11, an ejection tray unit 12, and acontrol unit 13. A sheet is conveyed by a conveying mechanism, includinga roller pair and a belt, along a sheet conveying path, which isindicated by a solid line in the drawing.

The sheet feeding unit 1 is a unit that retains and supplies acontinuous sheet wound into a roll. The sheet feeding unit 1 is capableof accommodating two rolls R1 and R2 and selects one of the rolls toreel out and feed the sheet. The number of rolls to be stored is notlimited to two and, instead, may be one roll or three or more rolls.

The decurling unit 2 is a unit that reduces the curling (warping) of thesheet fed from the sheet feeding unit 1. The decurling unit 2 uses onedriving roller and two pinch rollers to apply a decurling force to thesheet by warps the sheet in a direction opposite to that of the curling.The skew correction unit 3 is a unit that corrects the skew (inclinationrelative to the proper conveying direction) of the sheet that has passedthrough the decurling unit 2. The skew of the sheet is corrected bypushing a guide member against the edge of the sheet that is used as areference.

The printing unit 4 is a unit that forms an image on the sheet from thetop side of the conveyed sheet with the recording head 111. The printingunit 4 includes a plurality of conveying rollers that convey the sheet.The recording head 111 is a line print-head unit provided with an inkjetnozzle array that covers the maximum width of the sheet to be used. Therecording head 111 has a plurality of print heads arranged in parallelin the conveying direction. The inkjet method may be a method using aheater element, a piezoelectric element, an electrostatic element, or anMEMS element. Colored ink is fed from the ink tanks to the recordinghead 111 through corresponding ink tubes. The recording head 111 movesin the up-to-down direction on the sheet (z direction) to perform capoperation. Then, the recording head 111 moves in a directionperpendicular to the sheet (y direction). A mechanism that carries outsuch operation and a motor that drives the mechanism are provided.

An inspection unit 5 is a unit that optically reads inspection patternsand images printed on the sheet by the printing unit 4 and inspects thenozzle condition of the print heads, the sheet conveying condition, theimage position, and so on. The cutter unit 6 is a unit including amechanical cutter that cuts the printed sheet at predetermined lengths.The cutter unit 6 includes a plurality of conveying rollers that sendsout the sheet to the next process. The information recording unit 7 is aunit that records printing information, such as serial numbers and datesof the printing, on the back side of the cut sheet. The drying unit 8 isa unit that heats the sheet printed at the printing unit 4 to dry theapplied ink in a short amount of time. The drying unit 8 includes aconveying belt and a conveying roller that send out the sheet to thenext process.

The sheet winding unit 9 is a unit that temporarily winds the continuoussheet on which front-side printing has been completed in the duplexprinting mode. The sheet winding unit 9 includes a winding drum thatrotates to wind the sheet. The uncut continuous sheet on whichfront-side printing has been performed is temporarily wound by thewinding rotary member. When sheet is completely wound, the winding drumrotates in the reserve direction to send out the wound sheet and feedthe sheet to the decurling unit 2 from where the sheet is sent to theprinting unit 4. Since the sides of the sheet are reversed, printing canbe performed on the back side by the printing unit 4. Details of theoperation of duplex printing will be described below.

A reading unit 17 reads test patterns for maintenance of the printerheads printed at the printing unit 4. The ejection conveyance unit 10 isa unit that conveys the sheet cut at the cutter unit 6 and dried at thedrying unit 8 to the sorter unit 11. The sorter unit 11 is a unit thatsorts printed sheets into different groups, when required, intodifferent ejection trays of the ejection tray unit 12. The control unit13 is a unit that controls all units in the printing apparatus. Thecontrol unit 13 includes a CPU, a memory, a controller 15 having variousinput/output (I/O) interface, and a power source. The operation of theprinting apparatus is controlled on the basis of instructions from thecontroller 15 or an external device 16 of a host computer connected tothe controller 15 via an I/O interface.

Operation of Recording Medium During Simplex and Duplex Printing

Next, the basic operation during printing will be described. Since theprinting operations of a simplex printing mode and a duplex printingmode differ, each mode will be described below. FIG. 4 illustrates theoperation of a simplex printing mode. A sheet conveying path of thesheet being fed from the sheet feeding unit 1, printed, and ejected tothe ejection tray unit 12 is indicated by a heavy line in the drawing.Front-side printing is performed at the printing unit 4 on the sheet fedfrom the sheet feeding unit 1 and processed at the decurling unit 2 andthe skew correction unit 3. The printed sheet that has passes throughthe inspection unit 5 is cut into sheet pieces having a predeterminedlength set in advance in the cutter unit 6. Print information isrecorded on the back side of the cut sheet pieces by the informationrecording unit 7 as required. Each cut sheet piece is then conveyed tothe drying unit 8 and dried. The dried cut sheet pieces are sequentiallyejected through the ejection conveying unit 10 and stacked in theejection unit 12 of the sorter unit 11.

FIG. 5 illustrates the operation in the duplex printing mode. In theduplex printing mode, the back-side printing sequence is performed afterthe front-side printing sequence. The operations of the sheet feedingunit 1 through the inspection unit 5 in the front-side printing sequenceare the same as those in the above-described simplex printing sequence.The sheet is not cut by the cutter unit 6 and is conveyed to the dryingunit 8 as a continuous sheet. After drying the ink on the front side atthe drying unit 8, the sheet is guided to the path to the sheet windingunit 9 and does not enter the path to the ejection conveying unit 10.The guided sheet is wound up by the winding drum of the sheet windingunit 9, which is rotating in the forward direction (counterclockwise inthe drawing). When the planned front-side printing is completed by theprinting unit 4, the rear edge of the printing area on the continuoussheet is cut by the cutter unit 6. The continuous sheet on thedownstream side of the cutting position in the conveying direction(printed portion of the continuous sheet) passes through the drying unit8 and is entirely wound to its rear edge (cutting position) by the sheetwinding unit 9. Simultaneously, the continuous sheet remaining on theupstream side of the cutting position in the conveying direction isrewound by the sheet feeding unit 1 so that the front edge of the sheet(cutting position) does not remain in the decurling unit 2.

After the above-described front-side printing sequence is performed, theback-side printing sequence is performed. The winding drum of the sheetwinding unit 9 rotates in a direction opposite to the rewindingdirection (i.e., in the clockwise direction in the drawing). The edge ofthe wound sheet (the rear edge during winding is the front edge duringfeeding) is fed to the decurling unit 2. Decurling in the directionopposite to that described above is performed at the decurling unit 2.This is because the sheet wound around the winding drum has curls in theopposite direction since it is wound such that the front and back sidesare reversed compared to when the sheet is wound around the sheetfeeding unit 1. Then, the sheet is passed through the skew correctionunit 3 and printing is performed on the back side of the continuoussheet at the printing unit 4. The printed sheet that has passes throughthe inspection unit 5 is cut into sheet pieces having a predeterminedlength set in advance in the cutter unit 6. Since printing is performedon both sides of the cut sheet pieces, recording is not performed at theinformation recording unit 7. Each cut sheet piece is then conveyed tothe drying unit 8, sequentially ejected through the ejection conveyingunit 10, and stacked in the ejection unit 12 of the sorter unit 11.

Operation during maintenance including the above-described outputcorrection is the same as that of simplex printing. A test pattern formaintenance of the printer heads is printed at the printing unit 4 onthe sheet fed from the sheet feeding unit 1 and processed at thedecurling unit 2 and the skew correction unit 3. The printed sheet thathas passes through the inspection unit 5 is cut into sheet pieces havinga predetermined length set in advance in the cutter unit 6. Each cutsheet piece is then conveyed to the drying unit 8 and dried. Afterdried, the test pattern on each cut sheet piece is read at the readingunit 17. Then, each cut sheet piece is ejected through the ejectionconveying unit 10 and stacked in the ejection unit 12 of the sorter unit11.

System Configuration

FIG. 6 illustrates an example system configuration according to thepresent invention. The drawing illustrates the inkjet recordingapparatus main body 100 in FIG. 1 and a host PC 300 that sends printdata to the inkjet recording apparatus.

The host PC 300 mainly includes the following blocks. A CPU 301 carriesout processing on the basis of programs stored in an HDD 303 and a RAM302. The RAM 302 is a volatile storage and temporarily holds programsand data. The HDD 303 is a volatile storage and temporarily holdsprograms and data. A data transfer interface (I/F) 304 transmits andreceives data to and from the inkjet recording apparatus main body 100.Physical connection is established by USB, IEEE 1394, LAN, or the like.A keyboard mouse I/F 305 is an interface that controls human interfacedevices (HIDs), such as a keyboard and a mouse, and receives input froma user. A display I/F 306 displays an image on a display unit.

The inkjet recording apparatus main body 100 mainly includes thefollowing blocks. A CPU 311 carries out processing on the basis ofprograms stored in an ROM 313 and a RAM 312. The RAM 312 is a volatilestorage and temporarily holds programs and data. The ROM 313 is avolatile storage and temporarily holds programs and data. A datatransfer interface (I/F) 314 transmits and receives data to and from thehost PC 300. A head controller 315 supplies print data to the recordingheads that actually prints an image and controls the printing.Specifically, the head controller 315 may be designed to read necessaryparameters and data from predetermined addresses in the RAM 312. Whenthe CPU 311 writes necessary parameters and data at predeterminedaddresses in the RAM 312, the head controller 315 is started up to carryout the actual printing. An image processing accelerator 316 carries outimage processing at a speed faster than the CPU 311. Specifically, theimage processing accelerator 316 may be designed to read in necessaryparameters and data from predetermined addresses in the RAM 312. Whenthe CPU 311 writes necessary parameters and data in the predeterminedaddresses, the image processing accelerator 316 is started up to performthe actual printing. The image processing accelerator 316 is notabsolutely necessary and image processing may be carries out merely bythe CPU 311. A scanner 317 controls the inspection unit 5 and thereading unit 17, which are illustrated in FIG. 3, and stores read datato a RAM. Furthermore, the scanner 317 reads and analyzes color densityand performs color space conversion of the color space of the readingdevice, which is required for correcting the output characteristic ofthe recording apparatus. An LUT method may be employed or arithmeticprocessing may be performed for high-speed processing. A motor driver318 conveys the recorded paper and moves the recording head 111, whichis illustrated in FIG. 3, in the y and z directions.

Maintenance Operation

Next, the maintenance operation according to this embodiment will bedescribed. The maintenance operation according to this embodimentprevents a decrease in image quality due to a variation in the ejectingvolumes of the recording heads, a color deviation in multiple colors,which is described below, nonuniform reading by the scanner, unevendrying, and so on. Thus, in this embodiment, correction test patternsare recorded, and, from the colorimetry results thereof, color densitydata for generating correction data is acquired.

FIG. 7 illustrates a processing flow of the maintenance operationaccording to this embodiment. The processing starts from Step S701. InStep S702, a conditional judgment is made to determine whether amaintenance incident has occurred. Whether a maintenance incident hasoccurred is determined at power-on. By making the conditional judgmentafter performing self-diagnosis at power-on about whether maintenance isrequired, the downtime when maintenance is not required and theconsumption of recording paper and ink can be reduced. By providing auser interface that enables a user to instruct maintenance, themaintenability is improved. By performing maintenance by using a timerprovided in the apparatus at predetermined intervals through whichdegradation in the characteristics occur, the maintenability isimproved. Instead of basing the timing of performing maintenance on timeintervals, maintenance may be performed on the basis of the number ofink dots ejected by counting the number of ejected ink dots andperforming maintenance each time the number exceeds a threshold. When amaintenance incident has not occurred and maintenance is not required,Step S703 may be skipped to go to Step S704. When maintenance isperformed, in Step S703, an output correction value T⁻¹[Y] is calculatedthrough a method described below with reference to FIG. 9, and data isupdated. In Step S704, an output correction value T⁻¹[Y] based onpredetermined correction data is applied, and recording is performed. Anapplication example of the output correction value is illustrated inFIG. 8.

Image Processing Flow

FIG. 8 is a block diagram illustrating an example configuration of animage processing unit that carries out image processing for an inkjetprinter. An image processing unit 402 receives image data of a targetpixel to be image processed from an input unit 401 and outputs the imageprocessed image data to an output unit 409. The image processing unit402 includes an input-color converting unit 403, a multi-color shading(MCS) unit 404, an ink-color converting unit 405, a head shading (HS)unit 406, a tone reproduction curve (TRC) processing unit 407, and aquantizing unit 408.

The input-color converting unit 403 converts input image data to devicecolor-image data. The input image data is a color signal containingthree elements and is input with an information format indicating colorcoordinates in a color space coordinate system, such as sRGB for colorson a monitor. The input image is converted to device color-image data,which is a color signal containing three elements, through a knownmethod, such as matrix computation or three-dimension look-up table(LUT) processing described in Japanese Patent Laid-Open No. 10-13674. Ina three-dimension LUT, combinations of input image data (R, G, B) andconverted device color-image data (R′, G′, B′) are stored. For example,when color elements independently change in three steps, such as R=0,128, 255, G=0, 128, 255, and B=0, 128, 255, the table will contain atotal of 27 (3×3×3=27) combinations.

The MCS unit 404 corrects device the color-image data that has beeninput-processed and converted and outputs device color-image data withless color unevenness.

The ink-color converting unit 405 converts the MSC-processed devicecolor-image data to ink color data containing a plurality ink colorsignals. Specifically, the ink-color converting unit 405 receives thedevice color-image data and converts it to ink color data correspondingto the number of ink colors using a known method, such as matrixcomputation, three-dimension LUT processing, or under-color removal,described in Japanese Patent Laid-Open No. 10-13674.

For the printer illustrated in FIG. 1, since the recording head 111 hasa total of four recording heads, i.e., black 101, cyan 102, magenta 103,and yellow 104, the device color-image data is converted to ink colordata corresponding to four colors.

The HS unit 406 converts the input ink color data to ink color datacorresponding to the ejecting volume of the nozzles in each recordinghead for each ink color and outputs ink color data with less colordensity unevenness in single ink color recording. Head shading (HS) isperformed, specifically, using a known method, such as one-dimension LUTprocessing, which is described in Japanese Patent Laid-Open No.10-13674.

The TRC processing unit 407 receives HS processed ink color data andconverts the ink color data for each ink color to ink-dot number data.Tone reproduction curve processing is performed, specifically, using aknown method, such as one-dimension LUT processing, which is describedin Japanese Patent Laid-Open No. 10-13674.

The quantizing unit 408 receives the TRC processed ink-dot number data,performs quantization, and outputs quantized data. In quantization,various quantization levels, such as two-level and three-level throughsixteen-level, exist. Usually, during two-level processing, the CMYKink-dot number data items are each converted to 1-bit data with andwithout ink dots for each of the CMYK. As a method of quantization, aknown pseudo continuous tone processing, such as a dither matrix methodor an error diffusion method, is used. Instead, however, depending onthe use of the output image, simple quantization may be used. Thequantized ink data is sent to the output unit 409.

At the output unit 409, the different colored ink is ejected from thenozzles to record an image on a recording medium on the basis of thequantized ink data. Specifically, ink is ejected from the recordingheads 101 to 104, which are illustrated in FIG. 1, to record an image onthe recording paper 106.

The basic process of output value correction according to thisembodiment has been described above. According to the present invention,the order of the steps in the process is not limited to that describedabove and an LUT may be prepared for high-speed processing.

Characteristic Configuration: Segmented Printing

Next, a method of generating correction data for a recording head, whichis the characteristic configuration of the present invention, will bedescribed. As described above, since the ejecting volume of each nozzlediffers due to manufacturing tolerance of the recording head, image datacorresponding to each nozzle (each ejecting port) or to eachpredetermined unit of nozzles should be corrected. In this embodiment, atest chart containing a plurality of correction test patterns isrecorded on a recording medium and read by a reading device, such as ascanner, for colorimetry, and then, based on the acquired colorimetricresults, correction data is generated.

At this time, depending on the width of the recording heads and therecording medium, a test pattern corresponding to a desired number ofnozzles may not be acquired in one recording operation. The recordinghead 111 according to this embodiment takes into consideration conveyingerrors of the recording medium and frameless printing and, thus, has anozzle width of 12.9 inches, which is greater than the maximum feedingwidth, i.e., 12 inches, of the recording medium. Nozzles in an areahaving a width greater than 12 inches, which is the maximum feedingwidth of the recording medium, should be corrected. However, since thetest pattern is recorded with a maximum width of 12 inches, a testpatter for the nozzles requiring correction cannot be obtained. To dealwith such a problem, in the present invention, correction data fornozzles requiring correction is generated on the basis of a plurality ofcorrection test patterns formed through segmented printing in which therecording heads and the recording medium are disposed at differentrelative positions and a test pattern is recorded at each position.

According to the present invention, repeatability errors that occur whena plurality of test charts formed through segmented printing performedwith the recording heads and the recording medium disposed at differentrelative positions can be reduced. In an ideal system, normal printingcan be performed after output correction even when analysis resultsobtained by performing segmented printing at each relative position areused. However, after performing segmented printing, a noise componentother than a variation in the ejecting volume is generated beforeanalysis is performed. Hereinafter, such a noise component is referredto as “repeatability error.” When such repeatability errors cumulate, acolor difference occurs at the borders in a recorded image on whichoutput correction is performed using correction data prepared bysegmented printing. When the color difference exceeds the visual limit,it is visibly recognized as a flaw in the image. Such a repeatabilityerror is caused by nonuniformity in the properties of the recordingpaper surface, unevenness in air currents generated during high-speedconveying of the recording paper, a color density rise due to drying ofthe ink on the ink head surface, nonuniformity of the infrared heatersurface of the drier, unevenness in drying air, and/or unevenness indrying due to the nonuniformity in the properties of the recording papersurface. Furthermore, at the scanner that reads the test patterns,electrical noise is generated during photoelectric conversion or at ananalog circuit.

For analyzing an ejecting error in the recording head, such as amisdicharged nozzle, simply, it is determined whether a nozzle has adefect and if so, the position of the defected nozzle is determined.Therefore, the required precision for the difference between data itemsacquired through segmented printing is low. However, when the colordensity output characteristic is controlled, as in this embodiment,color density set by the ejecting characteristics, such as ejectingvolume and ejecting timing, should be analyzed at high precision, and,hence, the repeatability error becomes an issue. According to thepresent invention, by performing correction for each segmented printingoperation, such a repeatability error can also be reduced. Segmentedprinting will be described in detail below with reference to the flowchart in FIG. 9.

FIG. 9 illustrates the process in Step S703 in FIG. 7 of calculating theoutput correction value T⁻¹[Y]. In Step S901, the counter is cleared,and the processing is started. In Step S902, a segment number Nd isdetermined on the basis of the paper width of the recording medium inthe direction of the nozzle array of the recording head on whichmaintenance is to be performed and the nozzle width of the recordinghead. The segment number Nd is determined by the following expression.

segment number Nd=int(recording medium width/nozzle width+1.0) (where,int is rounded off)  (1)

Specifically, when recording paper having widths of 5 to 12 inches isused, the segment number Nd of a 5-inch wide recording paper is three,and the segment number Nd of a 12-inch wide recording paper is two.Maintenance can be performed on the entire nozzle width of the recordinghead even on paper with a small width, regardless of the problems ofpaper width and conveying error. Next, in Step S903, the recording headis moved to a predetermined position. Hereinafter, the position of therecording head relative to the recording medium is referred to as a headposition (HP). When the recording head is moved three times, thepositions are sequentially referred to as a head position 1 (HP1), ahead position 2 (HP2), and a head position 3 (HP3). In Step S904,processing required for uniform input color-image data I[Y] is carriedout, and correction test patterns are recorded on the surface of therecording paper. At this time, the test pattern recorded at the HP1 isreferred to as “first correction test pattern,” and the test patternrecorded at the HP2 is referred to as “second correction test pattern.”

FIG. 10A illustrates example correction test patterns. The followingdescription is based on 8-bit data in an RGB color space. (255, 255,255) represents white, (255, 255, 0) represents yellow, (255, 0, 255)represents magenta, and (0, 255, 255) represents cyan. An intermediatetone pattern may be printed when needed. Mixed color patches, such as atwo-level color, a three-level color, or a four-level color, which arecombinations of ink dots, may be used. In this embodiment, a one-levelcolor and a two-level color will be described since variation andfluctuation in the ejecting volume of ink nozzles can be accepted andthe printing volume of required test patterns can be optimized.

In Step S905, the reading unit 17, which is illustrated in FIG. 3, readsthe test chart recorded in Step S904 and measures each area on therecording paper to acquire color information B[Y]. At this time, thevalues obtained by reading the test chart should be analyzed todetermine which nozzles in the nozzle array of the recording headcorresponds to which values. In the past, it was difficult to determinethe positions of the nozzles or minute areas for correcting the nozzlesdue to influences of, for example, conveying errors and/or scanneraberration. In this embodiment, this problem is solved by recordingpatterns for detecting nozzle positions, as illustrated in FIG. 10B,simultaneously with the correction test patterns.

FIG. 10B is an enlarged view of pattern 106011 in the correction testpatterns illustrated FIG. 10A. A pattern 1101 is formed by uniform colorinput data. Position detection marks 1103 are provided near a pattern1102 for position detection of the read data. A mark 1104 is providedfor detecting the positional relationship with respect to a specificnozzle.

Edge searching is performed on the detection mark to calculatecoordinates. By selecting, in advance, a specific nozzle for printing aposition detection pattern, the relative relationship of the nozzleposition of the position detection pattern and the nozzle used forforming the reading pattern can be determined. In this way, the absoluteposition of the nozzle used for forming the reading pattern can becalculated.

The intervals of the position detection marks 1103 may be determined onthe basis of conveying precision and aberration of the scanner opticalsystem. To improve the precision, the pattern 1102 may be desirablyinterposed between the position detection marks 1103 and positiondetection marks 1107. When reliability of the position precision isrequired, such as in division analysis, it can be determined whether thewidth is greater than a predetermined value on the basis of edges 1105and 1106 of the position detection mark 1104 so as to achieve aprescribed position detection precision to cope with a defect, such asmisdicharge.

Preprocessing, such as shading correction of the scanner and/ortrimming, is performed on the information read by the scanner. Whenreading is possible with a resolution of at least the minimum unit inthe y direction in which output value correction is performed, it isdesirable to process data of a plurality of pixels at this stage sincethe influence of unreliable sudden noise and/or dust, such as poweredpaper attaching to the surface of the recording paper and/or the readingscanner, can be reduced. Addition or averaging is performed in an areasmaller than or equal to that required for output value correction.Since the output value correction is performed in the nozzle direction(y direction), it is desirable that the number of additions in the ydirection be different from the number of additions in the x direction.Taking into consideration the conveying precision in the x direction, itis desirable that the number of additions in the x direction not be thesame as the correction unit for adjoining areas.

After carrying out the above-described processing, luminance data isconverted to color density data. Conversion may be performed through logconversion or by using the characteristics of the scanner as a profile.

Next, in Step S906, the segment number and the number of processingoperation are compared, and a required number of processing operationsis carried out. When processing operations corresponding to the segmentnumber Nd is completed, the process proceeds to Step S907. In Step S907,the color information B[Y] acquired in segments is combined using themethod described below. Then, in Step S908, the displacement amount T[Y]in each area is determined for the entire width of the nozzles of therecording head on the basis of corresponding color information. In StepS909, the output correction value T⁻¹[Y] for the each area is calculatedfor the entire width on the basis of corresponding color information. InStep S910, the determined output correction is stored in the memory, andthe process ends.

Y-Movement Printing and Measurement

In step S907, a method of combining the color information B[Y] acquiredin segments will be described in detail below. FIGS. 11A and 11B areschematic views of the position of the recording head. FIG. 11Aillustrates the position of the recording head 111 in the y direction.FIG. 11B illustrates the position of the recording head 111 with respectto a recording medium 116. A state in which correction test patterns arerecorded using nozzles in the area a-c and areas b to d of the recordinghead 111 is illustrated. Among the nozzles disposed in the recordinghead 111, nozzles in the area a-c, which are continuously aligned fromthe edge a, are referred to as “first nozzle group (first ejecting portgroup). The position of the recording head at which recording isperformed using this nozzle group is referred to as “head position 1(HP1).” Similarly, nozzles in the areas b to d are referred to as“second nozzle group (second ejecting port group). The position of therecording head at which recording is performed using this nozzle groupis referred to as “head position 2 (HP2).” A test chart 117 is recordedat the HP1, and a test chart 118 is recorded at HP2. The scanner 317,which is the reading device according to this embodiment, is alsoprovided. To illustrate the position in the y direction, the scanner 317is adjacent to the recording head 111 in the x direction.

FIGS. 12A and 12B illustrate color-density-converted data obtained byscanning the test patterns in the test charts at the HP1 and the HP2.The horizontal axis represents the position of the recording head in they direction corresponding to the reading by the scanner. The verticalaxis represents color density. When test patterns of multiple colors andcolor density are recorded for a test chart, data sets corresponding tothe number of test patterns are prepared. FIG. 12A illustrates thecolorimetric result of the test patterns recorded at HP1, which is colordensity data recorded using the first nozzle group (first ejecting portgroup). Similarly, FIG. 12B illustrates the colorimetric result of thetest patterns recorded at HP2, which is color density data recordedusing the second nozzle group (second ejecting port group). Thepositions corresponding to nozzles in the area a-d on the recording headare illustrated.

The data acquired in segments is combined on the basis of the dataacquired by reading the test patterns. However, there is a problem inscanner reading in that the edge sections of the recording medium cannotbe read correctly because they are easily influenced by the base color.Accordingly, in this embodiment, the data segments are combined usingdata from positions where this influence at the edge sections of therecording medium can be ignored. This will be described with referenceto FIGS. 13A and 13B.

FIG. 13A illustrates color density data 131 of a test pattern at thecalculated HP 1 overlapping color density data 132 of a test pattern atthe calculated HP2. At each head position, nozzles in the area from b-cin the first and second nozzle groups are used redundantly. Nozzles inthe overlapping area b-c are referred to as “third nozzle group (thirdejecting port group). Based on color density data of the area recordedusing the third nozzle group, the color density data sets are combinedto generate correction data. In this embodiment, the area f-c at HP1represents an area in which reliability is not assured when reading therecorded test patterns with the scanner. This is the same for the areab-e at HP2. Thus, by combining the color density data sets of the areae-f, the influence on the edge sections of the recording medium can besuppressed. In this way, when recording test patterns in segments, suchan area in which reliability cannot be assured should be taken intoconsideration to desirably select the size of a recording medium suchthat redundantly used nozzles in the area b-c (third ejecting portgroup) are included.

When the color density data sets acquired through multiple recordingoperations do not match and differ greatly, accurate data cannot beacquired even when areas in which reliability is not assured whenreading with the scanner are avoided. In the area e-f in FIG. 13A, thereis a difference in the color density data 131 and the color density data132, which is due to the above-described repeatability error. Therepeatability error could be influenced by the ejecting precision ofink, the position precision of ejected ink being attached to therecording medium, variation of the surface of the recording medium,fluctuation in drying, fluctuation in scanner readings, and/orelectrical noise due to photoelectric conversion. In particular,unevenness in drying is caused by the position of printed ink,nonuniformity in the recording medium, and nonuniformity in heat windand infrared rays and tends to be highly random. The repeatability errordoes not cause a problem in quality when output correction is performedby recording the test pattern at once. However, aberration may begenerated when output correction is performed by combining test patternsrecorded through segmented recording performed multiple times.

According to this embodiment, a number of data sets required by theadditivity of variance of the randomly occurring causes is multiplied.

number of multiplications=(actual number of errors/desired number oferrors)²  (2)

In this embodiment, with respect to the desired number of errors, theactual number of errors can be estimated during product design from anS/N ratio due to noise, etc. In accordance with the estimated number,the required overlapping width is calculated. By allotting the number ofmultiplications in the x direction within a restricted range ofconveying precision, position detection, and correction, as describedabove, the resolution of the performance analysis correction of thenozzles can be prevented from being reduced. The required number ofadditions may be determined by measuring the actual use condition to setthe required overlapping width.

FIG. 14 illustrates a flow for correction according to this embodiment.First, analysis and correction are performed to correct therepeatability errors among the head positions (HPs). Then, edge-sectionprocessing is carried out for analysis and correction for reducingaberration generated at the joining section (nozzle overlapping areas)of the head positions (HPs).

The process begins in Step S1401. In Steps S1402 and S1403, thecharacteristic difference in the overlapping areas at the head positions(HP) is calculated. In this embodiment, a ratio is determined from theaverage value of color density data of the area e-f of the nozzles.

The color density data acquired by reading the patterns recorded at theHP1 is represented by D[P1][Y](a≦Y≦c). Similarly, the color density dataacquired by reading the patterns recorded at the HP2 is represented byD[P2][Y](b≦Y≦d). Here, Y represents the nozzle positions of therecording head in the y direction. Based on these color density datasets, the average value of the color density data in the area e-f at HP1is represented by Dave[P1][e-f], and the average value of the colordensity data in the area e-f at HP2 is represented by Dave[P2][e-f]. Theratio of the two average values is calculated, and a coefficient K isdetermined.

K=Dave[P1][e-f]/Dave[P2][e-f]  (3)

Next, in Step S1404, the determined coefficient K is multiplied by theentire nozzle area of the recording head. In this embodiment, theaverage value for HP2 is matched with the average value of HP1.

Dp1[P2][Y]=K×Dave[P2][Y]  (4)

Through this process, the color density difference between the HP1 andthe HP2 can be decreased.

By performing correction by calculating the ratio in this way, colordensity differences due to, for example, a difference in the dynamicrange due to drying or a difference in the luminance signals of thescanner, can be reduced. The influence of causes, such as a dark currentof a sensor and drifting of an analog circuit, can reduced bycalculating the difference of Expressions 5 and 6 to determine acoefficient K′ and adding this to the entire nozzle area of therecording head at the HP2.

K′=Dave[P1][e-f]−Dave[P2][e-f]  (5)

Dp1[P2][Y]=K+D[P2][Y]  (6)

Here, Y represents the nozzle position of the recording head at the HP2in the y direction.

The analysis and correction for correcting the repeatability error ofcolor density data of different head positions (HPs) has been describedabove. In this way, by adding the overlapping area of the color densitydata at the HP1 and HP2 to the entire area, the influence of light fromthe MTF of the optical system and scattered light from illumination isalso reduced when the edge sections of the test chart is read by thescanner.

Next, correction performed when the color density data sets in theoverlapping area is combined will be described with reference to FIG.13B. Since the repeatability error is decreased in Step S1404, theaverage color densities of the nozzles in the overlapping areas at thehead positions match. However, a noise component that remains due tocauses other than the repeatability error and that occur duringrecording and analysis at each head position causes a differencedepending on the position of the recording head in the y direction. Suchcauses other than the repeatability error may be nonuniformity in dryingand the scanner, in addition to randomly occurring causes. Since theaverage color densities match as a result of correcting therepeatability error, there is no problem in using an analysis valueobtained at any one of the head positions. However, at the border ofeach head position, when a noise component having low level ofcorrelation with noise generated at each head position is included, thechange becomes discontinuous, and a correction error could cause adefective image. Thus, in the overlapping area, at a position b, whichis the border of the HP1, the data of the HP1 is weighted, and at aposition c, which is the border of the HP2, the data of the HP2 isweighted.

In Step S1406, to reduce the aberration generated in the area b-c,weighted averaging by the ratio corresponding to the position in the ydirection is performed on the color density data for the recording headat each head position.

Dwa[Y]=αD[P1][Y]+(1−α)Dp1[P2][Y] (0≦α≦1, b≦Y≦c)  (7)

Here, when Y=b, α=1, and when Y=c, α=0.

As described above, the corrected color density data D[Y] is calculatedfrom the position Y in the y direction as indicated below (Step S1407).

$\begin{matrix}{{D\lbrack Y\rbrack} = \left\{ \begin{matrix}{{D\left\lbrack {P\; 1} \right\rbrack}\lbrack Y\rbrack} & \left( {a \leqq Y < b} \right) \\{{Dwa}\lbrack Y\rbrack} & \left( {b \leqq Y \leqq c} \right) \\{{Dp}\; {{1\left\lbrack {P\; 2} \right\rbrack}\lbrack Y\rbrack}} & \left( {c < Y \leqq d} \right)\end{matrix} \right.} & (8)\end{matrix}$

The above-described processing is carried out on one color-value dataset among the uniform input image recorded in Step S904.

Thus, Dn[Y] is determined for all test patterns by carrying outprocessing for all bands in all test patterns (Step S1408). Then, B[Y]is calculated on the basis of D1[Y], D2[Y], . . . Dn[Y], which arecorrected with corresponding patches. In this embodiment, since Dn[Y] iscolor density data, and B[Y] is luminance data, post-processing of logconversion for converting the color density data to luminance data isperformed (Step S1409). Then, the process is ended (Step S1410).

As described above, in this embodiment, correction for reducingrepeatability error and correction of decreasing errors, such asunevenness in drying and reading errors of the scanner, that cannot bedecreased by repeatability error are performed. By weighting the colordensity data at the head position when combining the color density datasets corresponding to the area of redundantly used nozzles, a reductionin image quality caused by aberration occurring in the correction resultcan be suppressed, and appropriate correction can be performed.

As described above, it is desirable to select the size of the recordingmedium on which the correction test patterns are recorded such that thearea b-c, which is an overlapping area, is set as long as possible. Thefollowing relationship stands:

Δ/dy=tan Θ  (9)

where Δ represent a change in the color density difference, tan Θrepresent the gradient, and dy represent the length in the y directionin which change occurs. That is, as the more gradual the change, i.e.gradient, becomes, the more visually difficult the detection becomes.Therefore, it is desirable that the change Δ becomes small or changeoccurs in a section long in the y direction. Thus, the required lengthdy can be determined from the relationship between the generated colordensity difference (change Δ) and tan Θ. With respect to dy, the longerthe overlapping area is, the more effective the relaxation processing bythe above-described weighted averaging becomes.

By setting the unit of the position Y to a minimum unit for performingcorrection in the y direction, the processing data can be reduced.However, the unit of the position Y depends on the cause of changerequiring correction. Detection correction of the ejecting volume ofeach nozzle is performed per nozzle, whereas correction of thecharacteristic of the heater driving the nozzles is performed perheater. Furthermore, correction of the characteristic of the head chipis performed per head chip, whereas correction of the coolingcharacteristics of the ink supplying system is performed per ink supplychannel. By setting the size to a size that cannot be visibly resolved,an excessive amount of high resolution data is prevented from beingprocessed.

In this embodiment, rolled paper is used. Instead, however, cut papermay be used. In this embodiment, recording is performed by conveying therecording medium, instead of scanning the recording head. However, thepresent invention is not limited thereto. That is, so long as scanningis performed relatively to the recording head and the recording medium,the recording head may be scanned with respect to the recording mediumto perform recording. At this time, the scanning direction of therecording medium is a direction intersecting with the direction of thenozzle array of the recording head.

In this embodiment, the recording head ejects ink of four colors, C, M,Y, and K. However, the recording head is not limited thereto, and arecording head that ejects ink of colors such as light cyan (Lc), lightmagenta (Lm), light yellow (Ly), and gray (Gy) may be used. Moreover,the recording head 111 has four recording heads 101 to 104, whichrespectively eject CMYK ink. However, instead, a single recording headthat ejects ink of multiple colors may be used.

In this embodiment, the inkjet recording apparatus main body 100includes the scanner 317. However, instead, a scanner may be providedseparately from the recording apparatus, and the recording apparatus mayreceive the measurement results. The process of generating correctiondata may be performed by either the inkjet recording apparatus main body100 or the host PC 300, and parts of the processing may be performed byeither one.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-251900 filed Nov. 10, 2010, which is hereby incorporated byreference herein in its entirety.

1. An inkjet recording apparatus configured to record an image on arecording medium by ejecting ink while relatively scanning a recordinghead with respect to the recording medium in a direction intersectingthe predetermined direction, the recording head having a plurality ofejecting ports for ejecting ink arranged in a predetermined direction,the apparatus comprising: a first correction-test-pattern recording unitconfigured to record a first correction test pattern using a firstejecting port group of ejecting ports continuously aligned from a firstedge of the recording head, the number of ejecting ports in the firstejecting port group being smaller than the number of the ejecting portsof the recording head; a second correction-test-pattern recording unitconfigured to record a second correction test pattern using a secondejecting port group of ejecting ports continuously aligned in thepredetermined direction, part of the ejecting ports in the secondejecting port group being selected from the ejecting ports in the firstejecting port group and from ejecting ports not included in the firstejecting port group; and a correction-data generating unit configured togenerate correction data for correcting the image data corresponding toejecting ports included in the first ejecting port group and the secondejecting port group on the basis of a colorimetric result of the firstcorrection test pattern and a colorimetric result of the secondcorrection test pattern.
 2. The inkjet recording apparatus according toclaim 1, wherein the correction-data generating unit generatescorrection data for correcting image data corresponding to a thirdejecting port group including ejecting ports included in both the firstejecting port group and the second ejecting port group on the basis ofthe colorimetric result of the first correction test pattern and thecolorimetric result of the second correction test pattern.
 3. The inkjetrecording apparatus according to claim 2, wherein the correction-datagenerating unit generates correction data for correcting ejecting portsincluded in the third ejecting port group by changing weighting on thebasis of the colorimetric result of the first correction test patternand the colorimetric result of the second correction test pattern. 4.The inkjet recording apparatus according to claim 3, wherein thecorrection-data generating unit generates correction data for correctingpredetermined ejecting ports included in the third ejecting port groupsuch that weighting based on the colorimetric result of the secondcorrection test pattern is greater than weighting on correction data forcorrecting ejecting ports included in the third ejecting port group andcloser to the first edge than the predetermined ejecting ports.
 5. Theinkjet recording apparatus according to claim 2, wherein thecorrection-data generating unit generates correction data aftercorrecting at least one of the colorimetric result of the firstcorrection test pattern and the colorimetric result of the secondcorrection test pattern on the basis of a difference between thecolorimetric result of the first correction test pattern correspondingto the third ejecting port group and the colorimetric result of thesecond correction test pattern.
 6. The inkjet recording apparatusaccording to claim 1, wherein the correction-data generating unitgenerates correction data for each ejecting port.
 7. The inkjetrecording apparatus according to claim 1, further comprising: anacquiring unit configured to acquire a colorimetric result by performingcolorimetry on the first correction test pattern and the secondcorrection test pattern.
 8. An inkjet recording method of recording animage on a recording medium by ejecting ink while relatively scanning arecording head with respect to the recording medium in a directionintersecting the predetermined direction, the recording head having aplurality of ejecting ports for ejecting ink arranged in a predetermineddirection, the method comprising the steps of: recording a firstcorrection test pattern using a first ejecting port group of ejectingports continuously aligned from a first edge of the recording head, thenumber of ejecting ports in the first ejecting port group being smallerthan the number of the ejecting ports of the recording head; recording asecond correction test pattern using a second ejecting port group ofejecting ports continuously aligned in the predetermined direction, partof the ejecting ports in the second ejecting port group being selectedfrom the ejecting ports in the first ejecting port group and fromejecting ports on the recording head not included in the first ejectingport group; and generating correction data for correcting the image datacorresponding to ejecting ports included in the first ejecting portgroup and the second ejecting port group on the basis of a colorimetricresult of the first correction test pattern and a colorimetric result ofthe second correction test pattern.